1. The Field of the Invention
The present invention relates to the transmission of optical signals in a network. More particularly, the present invention relates to optical repeaters and more specifically to scalable transceiver based optical repeaters.
2. Background and Relevant Art
An underlying problem of optical networks is that optical signals carried by the optical networks are degraded during transmission for a wide variety of reasons. Signal noise, signal loss, signal attenuation, chromatic dispersion, and modal dispersion are examples of the deleterious effects experienced by optical signals in optical networks. Because optical signals degrade during transmission, the distance that an optical signal can be transmitted is limited. In addition, optical signals can only be transmitted a certain distance that may be related, for example, to the type of optical fiber (single mode, multi-mode, e.g.), the type of laser (Distributed Feedback Laser, Vertical Cavity Surface Emitting Laser, e.g.), type of data modulation, and the wavelength of the transmitted signal.
The distance that an optical signal can be transmitted can be increased using optical amplifiers such as erbium doped fiber amplifiers and semiconductor optical amplifiers. In fact, optical amplifiers can often be cascaded to increase the distance that optical signals can be transmitted. Without optical amplifiers, the ability to transmit optical signals could be limited. In spite of these advantages, optical amplifiers have several drawbacks that need improvement.
For example, optical amplifiers are often analog in nature and they therefore introduce noise into the optical signals. As noise is added to an optical signal, the likelihood of introducing errors or of being unable to read the optical signal increases. The problem of added noise becomes more pronounced when optical amplifiers are cascaded, because the noise accumulates at each optical amplifier. As a result, each subsequent optical amplifier, in addition to introducing new noise to the optical signal, amplifies the noise that was added by prior optical amplifiers. The addition of noise and the amplification of the added noise ultimately results in a corrupted optical signal.
In addition, the optical signal being amplified may include more than one channel (or wavelength of light), as is the case in Coarse Division Wavelength Multiplexing (CWDM), Dense Division Wavelength Multiplexing (DWDM), and other WDM systems. Unfortunately, optical amplifiers do not always provide the same amount of gain to each channel included in the optical signal. As a result, care must be taken to ensure that the gain of each channel is equalized or the distance that a particular optical signal can be transmitted decreases. In addition, the input of an optical amplifier should be within a particular range of optical power. Thus, optical amplifiers are often accompanied with variable optical attenuators to ensure that the optical signals are within the appropriate range.
Another problem associated with optical amplifiers is that they often lack scalability. Optical amplifiers, as noted above, are often configured to amplify more than one wavelength of light. When an optical amplifier fails, all of the channels of the optical signal are adversely affected. The optical amplifier cannot be fixed, but likely needs to be replaced. In other words, optical amplifiers are not pluggable.
Optical amplifiers are also unable to reset the jitter budget of an optical signal. In fact, this is one of the reasons that optical amplifiers, when cascaded to repeat optical signals, ultimately fail. The jitter budget is exhausted and the optical signal can no longer be recognized.